The present invention relates to a matrix printer particularly a matrix line printer wherein a back and forth or reciprocating member such as a shuttle carrying the print elements is of light-weight construction.
Matrix printers of the type to which the invention pertains usually include drive elements for the dot printing elements and being mounted on the shuttle. These drive elements usually are of electromagnetic design. The print elements are operated by a logic curcuit and a power drive circuit and cables connect them to that energizing and control circuit of the printer. These cables are constructed for example, as flexible strips or ribbon cable.
The logic circuit, broadly understood, includes or is connected to a symbol generator so as to obtain the proper combination dot printing action. In addition, the shuttle is, for example, guided by means of rollers which are suitably journalled in the frame of the printer and extend in parallel to the direction of shuttle motion. The European Pat. No. 8,411,106, which has been published subsequent to the date of priority of the present application, (see also U.S. application Ser. No. 777,538 filed Sept. 18, 1985 by me and another inventor) is descriptive of this kind of matrix printer but does not constitute a state of the art. However, the present application is to be seen as an improvement and further extension of the matrix printer as per said European patent application.
Printers of the type to which the invention pertains include, for example, solenoid drives for the print elements, the latter being for example, needles or styli. The print element carrier or shuttle can in fact be considered an oscillating device, the oscillations to occur along the print medium. Following the printing of a line of dots, the print medium is moved transversely to both the direction of styli movement as well as the direction of shuttle movement, by a very small spacing that is equivalent to a vertical dot distance.
The print element carrier and shuttle is of lightweight construction as stated and the individual print elements should also have a low mass. The needle bank (needles plus solenoid drives), so to speak and as carried by (or being part of) the shuttle, consumes a certain amount of electric power. That power is of course not completely converted into "printing power", but certain losses occur. These losses actually heat the print elements, and the thermal energy will flow primarily into the metallic shuttle. During extensive use and long time of printing, the shuttle will become quite warm, and, therefore, must be expected to expand physically. Consequently, the shuttle will undergo a certain physical expansion in accordance with certain basic laws of physics. This expansion however may entail for one reason or another and having to do with the mounting and the overall construction, a certain deformation of the shuttle. Owing to the minuteness of the various spacings involved, even a relatively small relative thermal expansion between or among the print elements cannot be tolerated, if specifically the spacing of the dots as printed varies on account of these thermal activities. These changes are usually not immediately noticeable but, say, after several hours of printing it has been observed that the appearance of the printing varies and usually deteriorates. To the best of my knowledge, no known features exist to prevent this kind of distortion and to adequately protect the shuttle i.e. the print element carrier against these thermally induced distortions.